High shear stress in venules where leukocyte/endothelial interactions and extravasation largely occur results in the requirement for specialized adhesion mechanisms to insure that arrest and migration of leukocytes can occur appropriately during an immune response. The specificity and regulation of this adhesion results from the various types of adhesion receptors that act in sequential fashion. The initial event of primary (rolling) adhesion has been attributed to the interaction between selectin receptors and their carbohydrate ligands on endothelial cells, while secondary (firm) adhesion is due to the integrin receptors interacting with their endothelial cell ligands. The investigator has characterized a novel primary lymphocyte/endothelial cell interaction in a parallel plate flow assay design to approximate postcapillary flow which is mediated by "activated" CD44 on the lymphocyte and hyaluronan on the surface of the endothelial cell. Unlike other types of lymphocyte traffic characterized at the molecular level for secondary lymphoid tissue, they propose that this primary adhesion is utilized generally at sites of chronic inflammation, as exemplified by rheumatoid arthritis and/or other chronic autoimmune diseases. Proposals include to study the mechanisms of CD44 activation enabling hyaluronate dependent rolling and regulation of hyaluronan expression on vascular endothelium, and to explore their expression in vivo in the vascular beds of tissues in which this interaction may operate. Three animal models of inflammation including adjuvant arthritis in rats, collagen induced arthritis in mice, and induced psoriasis in mice, will be used. The models will be evaluated for the extent of CD44 involvement in extravasation of lymphocytes from peripheral blood into joints or skin as well as regulation of CD44 expression on lymphocytes and hyaluronan expression in vascular beds. The mechanisms mediating both primary and secondary adhesion pertinent to this adhesion pathway will be studied using cells lines transfected with CD44 exhibiting variations in primary and/or secondary adhesion phenotype. In addition, the involvement of this adhesion interaction in human inflammatory processes will also be studied, with an emphasis on patients with autoimmune disease. With these studies the proposal aims to determine new methods for intervening in the often detrimental effects of this kind of lymphocyte traffic.